2D-Seed-Induced Crystallization Strategy Contributes to Blade-Coating FAPbI₃-Based Perovskite Solar Cells

Formamidinium lead iodide (FAPbI₃)-based perovskites are promising photoabsorber materials owing to their optimal bandgap and excellent photothermal stability. However, their complex crystallization behavior during blade-coating presents challenges for scalable fabrication, leading to poor perovskite film morphology and uniformity, which adversely affect the performance and stability of perovskite solar cells (PSCs). Herein, a two-dimensional (2D) perovskite seed layer was introduced onto the SnO₂ electron transport layer within a conventional n-i-p device architecture. This seed layer was employed to provide heterogeneous nucleation sites for and to induce the bottom-up-oriented growth of [PbI₆]^4- octahedra, thereby facilitating the formation of the photoactive α-FAPbI₃ phase with enhanced crystallinity and film uniformity. As a result, PSCs with an active area of 2.5 × 2.5 cm² were fabricated, achieving a power conversion efficiency (PCE) of 22.03% and an open-circuit voltage (V_OC) of 1.10 V. Furthermore, over 80% of the initial efficiency was retained after 2000 h of ambient storage (relative humidity ≈ 5%, temperature ≈ 25 °C) without encapsulation, indicating excellent long-term stability. Through this approach, a viable and scalable pathway has been established for the fabrication of high-quality α-FAPbI₃ films, offering significant potential for the advancement of efficient and stable PSCs.